Ribbon for non-impact printing of magnetic ink

ABSTRACT

The present invention relates to a ribbon for non-impact printing of documents of the type handled by magnetic reader/sorter apparatus comprising a polycarbonate substrate and a magnetic ink layer with a thin film of metal disposed between said substrate and said ink layer. The substrate consists essentially of a polycarbonate polymer containing from about 20 to about 40 percent by weight of an electrically conductive carbon black and the magnetic ink consists essentially of from about 60 to about 80 parts by weight of a solvent comprising at least member selected from the group consisting of aliphatic alcohols having from 1 to about 5 carbon atoms, and aromatic hydrocarbons having from about 6 to about 10 carbon atoms; about 10 to about 30 parts by weight of a polyamide polymer; from about 10 to about 30 parts by weight of a magnetic oxide; from about 1 to about 4 parts by weight of a plasticizer selected from the group consisting of azelate, phthalate, palmitate and adipate esters, from about 0 to about 10 parts by weight of carbon black and from about 0 to about 5 parts by weight of an alcohol soluble dye.

BACKGROUND OF THE INVENTION

The present invention relates to ribbons for non-impact printing andmore particularly to ribbons for non-impact printing of magnetic inkcompositions to encode checks and other machine readable documents.

So called "non-impact printing" as a broad concept is now well known inthe art. It has become a more and more popular means of printing intypewriters, computer printers and the like because of the eliminationof the very high noise associated with impact technologies such as dotmatrix and daisy wheel systems. The basic principle of the non-impactprinting is the use of heat to melt an ink coating from the ribbon toform an image on a receiver substrate such as paper.

The conventional thermal transfer process employs a thermal printheadwhich is a resistor, and the ribbon is composed of a substrate ofpolyester film with a wax ink coating applied to one side. The printheadgenerates a thermal energy which comes in contact with the polyester.The heat is transmitted from the printhead through the polyester to thewax ink coating which melts to form the image. The thermal printheadmust, of course, be cooled down and reheated for each separate imageformation.

A more recent non-impact system, often referred to as an electricallyresistive heat transfer system differs from the conventional thermaltransfer system both in printhead and in ribbon construction. Using thistechnology, the printhead is not a resistor and does not itself generateheat per se, but rather is composed of a plurality of thin wires orelectrodes which pass on electrical current. The heat needed forproduction of the image is generated within the ribbon itself by theelectrical current from the printhead. Thus, the ribbon itself is ineffect the resistor and normally comprises three layers, a conductivepolymer film which will serve as a resistor with respect to the electriccurrent and thereby generate heat; a thin layer of metal such asaluminum usually applied by vacuum deposition techniques; and the thirdink containing meltable polymer based layer which will melt in responseto the heat generated in the polymer film, and transfer from the metallayer to the substrate in the form of the desired image. An additionalrelease layer is sometimes employed between the aluminum and the inklayer to further facilitate the transfer of the ink to the substrate.

The electrically resistive heat transfer techniques have a number ofsignificant advantages over so-called conventional thermal transfertechniques. First, they substantially lower the printer costs, sincethey eliminate the necessity for expensive components to cool and reheatthe printhead. Also, they facilitate higher printing speeds since theydon't require a conventional resistor thermal printhead which must becooled down and reheated between images. And, perhaps most important,these new techniques can generate better print quality, since the heatis generated within the ribbon itself and is not dissipated by goingthrough intermediate layers, thereby providing better print quality overa much wider range of papers, films and other substrates.

To date, however, the materials employed in the ink layer ofelectrically resistive heat transfer ribbons have consisted primarily ofpigments such as carbon black and other inorganic materials.

For example, U.S. Pat. No. 4,103,066 discloses a ribbon for non-impactprinting which comprises a transfer layer and a substrate. The substrateis a polycarbonate resin containing from about 15 to about 40%electrically conductive carbon black and the transfer coating is made upof wax, carbon black and a dye such as methyl violet dye. U.S. Pat. No.4,549,824 discloses the use of azo dyes in thermal ink transferapplications, but these dyes facilitate the use of lower temperaturesrather than providing erasure proof print characters on the ultimatesubstrate.

While the inks and ribbons heretofore known are quite satisfactory intypical conventional typing and printing applications of most businessoffices, they are often unsuited for applications such as the printingof checks, negotiable instruments and other special documents of thetype which should, if possible, be erasure proof and which can only beexpeditiously handled by sophisticated magnetic reader/sorter equipment.These applications have not heretofore been open to the use ofelectrically resistive heat transfer techniques, instead requiring muchslower and extremely noisy impact printing techniques.

In the so-called typical office applications, the criteria for settingminimum standards of clarity and quality are often largely subjectivejudgments left to the individual typing or printing the document and,accordingly, a high degree of variation exists. In the printing ofdocuments to be sorted by magnetic reader/sorter equipment, however, thestandards are extremely detailed, and critical image standardsestablished by the American Banking Association for magnetic encodedimages must be met.

Typical ribbons used today for impact printing of checks, negotiabledocuments, and the like, generally have an ink coating which is on theorder of 65% or more magnetic oxide. Such a loading of magnetic oxidehas been considered essential to obtain both visual print quality andthe desired level of signal transmission for machine scanning. Yet suchloadings are clearly impossible in thermal transfer applications, wherethe ink layer must melt and transfer to the paper or document substrate,because the melting points of the magnetic oxides are several orders ofmagnitude higher than the general limit at 150° C. required to avoidmelting the electrically resistive polymer substrate.

It is therefore, one object of the present invention to provide a ribbonfor non-impact magnetic printing of checks and other documentstraditionally handled and processed with the aid of magneticreader/sorter equipment.

It is another object of the present invention to provide a magnetic inkcomposition useful in encoding checks and similar documents processedwith the aid of magnetic reader/sorter apparatus.

It is yet another object of the present invention to provide a ribbonfor non-impact erasure proof printing of checks and other negotiabledocuments.

SUMMARY OF THE INVENTION

It has now been discovered that it is possible to provide asubstantially erasure proof "magnetic transfer ribbon" for use withelectrically resistive heat transfer equipment. The ribbon is composedof a electrically resistive polymer layer and a layer containingmagnetic ink and erasure proof dye, plus a thin layer of metal disposedbetween said resistive layer and said ink layer.

In one aspect, the present invention comprises a magnetic ink fornon-impact printing of documents which are normally processed usingmagnetic reader/sorter equipment. The ink consists essentially of fromabout 60 to about 80 parts by weight of a solvent comprising at leastmember selected from the group consisting of aliphatic alcohols havingfrom 1 to about 5 carbon atoms, and aromatic hydrocarbons having fromabout 6 to about 10 carbon atoms; about 10 to about 30 parts by weightof a meltable polymer; from about 10 to about 30 parts by weight of amagnetic oxide; from about 1 to about 4 parts by weight of a plasticizerselected from the group consisting of dioctyl azelate, dioctylphthalate, dodecyl azelate, diisooctyl azelate, butyl stearate,isopropyl palmitate, and similar esters, fatty acids and the like. Theink may also contain from about 0 to about 10 parts by weight of carbonblack and from about 0 to about 5 parts by weight of an alcohol solubledye.

In another aspect, the present invention comprises a ribbon fornon-impact printing of documents of the type handled by magneticreader/sorter apparatus comprising the above described magnetic ink anda polycarbonate substrate with a thin film of metal disposed betweensaid substrate and said ink layer; said substrate consisting essentiallyof a polycarbonate polymer containing from about 20 to about 40 percentby weight of an electrically conductive carbon black.

In yet another aspect the present invention comprises ribbon fornon-impact erasure proof printing of documents such as checks negotiableinstruments and the like comprising a polycarbonate substrate and ameltable ink layer with a thin film of metal disposed between saidsubstrate and said ink layer. The substrate consists essentially of apolycarbonate polymer containing from about 20 to about 40 percent byweight of an electrically conductive carbon black. The meltable inkconsists essentially of from about 50 to about 80 parts by weight of asolvent comprising at least member selected from the group consisting ofaliphatic alcohols having from 1 to about 5 carbon atoms, and aromatichydrocarbons having from about 6 to about 10 carbon atoms; about 10 toabout 30 parts by weight of a polyamide polymer; from about 10 to about30 parts by weight of a magnetic oxide; from about 1 to about 4 parts byweight of a plasticizer selected from the group consisting of azelate,phthalate, palmitate and adipate esters; from about 1 to about 10 partsof an alcohol soluble dye, and from about 0 to about 10 parts by weightof carbon black.

PREFERRED EMBODIMENT

In the preferred embodiment of the present invention, the ribboncomprises a polycarbonate polymer substrate having a thickness of fromabout 10 to about 20 microns, a thin film of aluminum having a thicknessof from about 800 to about 1200 angstroms, preferably applied to thepolycarbonate substrate by vapor deposition techniques, and an ink layerhaving a melting point below that of the polycarbonate substrate and athickness of from about 5 to about 20 microns. The preferred inkcomposition consists essentially of from about 50 to about 80 parts byweight of a solvent comprising at least one member selected from thegroup consisting of aliphatic alcohols having from 1 to about 5 carbonatoms, and aromatic hydrocarbons having from about 6 to about 10 carbonatoms; about 10 to about 30 parts by weight of a polyamide polymer; fromabout 10 to about 30 parts by weights of a magnetic oxide; and fromabout 1 to about 4 parts by weight of a plasticizer such as dioctylazelate, dioctyl phthalate, dodecyl azelate, or the like. The inkcompositions may optionally contain 1/2 part by weight or more of carbonblack and/or 1/2 part by weight or more of an alcohol soluble dye.

It will, of course, be appreciated that a wide degree of latitude exitsin the selection of specific solvents. The function of the solvent is toprovide a substantially uniform viscous mixture which can be screened,rolled or applied by other well known means on to the aluminum coatedpolycarbonate substrate. The solvent, of course, must be miscible and/orcompatible with the other components of the ink, must have a boilingpoint high enough to assure that there is no undue loss of solvent priorto application of the ink layer to the aluminized polycarbonate ribbon,yet sufficiently low to assure that most of the solvent will beevaporated during fabrication of the ribbon so that the fabricatedribbon will be effectively dry to the touch.

The plasticizer on the other hand may be selected from a wide variety ofaromatic and aliphatic oils compatible with the polyamide or otherpolymer resin being used in compounding the ink. It must have a boilingpoint higher than the temperature being transmitted through the metallayer to the ink layer. In general, any plasticizer commonly employedwith the polymer utilized in the ink composition should prove suitable.The original function of the plasticizer was to improve the flow at themelt point, but it has been very surprisingly found that it alsosubstantially improves print quality and the level of the signaltransmission.

The following examples as well serve by way of illustration and not byway of limitation to describe some of the preferred ribbons and inkcompositions of the present invention.

EXAMPLE 1

An ink composition was prepared by admixing the following ingredients:

    ______________________________________                                        Isopropyl Alcohol     49 parts by weight                                      Toluene               20 parts by weight                                      UNIREZ 1533         15.5 parts by weight                                      Polyamide Resin                                                               (Union Camp)                                                                  Hercules B-350 Grade                                                                              17.5 parts by weight                                      Magnetic oxide                                                                Carbon Black          1 part by weight                                        Di-octyl azelate      4 parts by weight                                       Nigrosine Alcohol     1 part by weight                                        Soluble Dye                                                                   ______________________________________                                    

The ingredients were mixed for 16 hours at 25° C. in ball mill. Themagnetic ink composition was applied to the aluminized side of a carriersubstrate with a reverse roll coater. The carrier substrate was MobayChemical Corporation MAKROFOL KL3-1009, prepared from a polycarbonatefilm and conductive carbon black, milled in methylene chloride and castcoated on a metal drum; (Caliper, 15 microns +/-5%; Tensile Strength,9,500-11,000 psi; Elongation, 9%; Surface Resistance, 580-650 ohm sq.;Volume Resistivity, 1 ohm-cm; and a Density of 1.28); which was castinto a substrate film 24 inches wide by 15 microns thick, onto onesurface of which a 1000 Å layer of aluminum was applied by conventionalvapor deposition techniques.

The assembled ribbon was employed in conjunction with a standardcommercial IBM Quietwriter printer (Model 5201) to magnetically imprinta series of test documents. The magnetically imprinted documents werethen processed in a Unisys magnetic reader/sorter and a reject rate ofless than 1% was observed. These results are highly unexpected in asmuch as the normal magnetic oxide loading of over 65% has been reducedto about 16% of the total ink composition, and less than 45% of the nonvolatile portion of the ink.

EXAMPLE II

Two additional test ribbons were prepared in a manner similar to ExampleI, but using the following ink formulations.

    ______________________________________                                                            % Wt.                                                     ______________________________________                                        Formula A                                                                     Polyamide Resin (Unirez 1533)                                                                       19                                                      Isopropyl Alcohol     53                                                      Toluene               23                                                      Carbon Black           5                                                      Formula B                                                                     Polyamide Resin (Unirez 1533)                                                                       19                                                      Isopropyl Alcohol     53                                                      Toluene               23                                                      Alcohol Soluble Nigrosine Dye                                                                        5                                                      ______________________________________                                    

Each of the foregoing formulas was employed to produce a test ribbonwhich was employed in test printing using Quietwriter equipment asdescribed in Example 1. The documents produced by each of the tworibbons were subjected to erasure testing. The print produced by FormulaA was readily mechanically erased with a simple pencil eraser. The printproduced from Example B on the other hand could not be completely erasedwithout disruption of the paper fiber which would make it obvious thatan erasure had taken place. Further examination of the print produced byFormula B indicated that the dye had been carried into the paper fibersapparently by residual solvent. It will, of course, be obvious that forapplications such as those contemplated for the printing ribbons of thepresent invention, the ability to provide an erasure proof printcharacter is extremely advantageous and desirable.

A series of further tests were conducted to evaluate the optimum loadinglevel for magnetic oxide and optimum plasticizer level. In general, itwas found that compositions in which the ratio of polyamide resin tomagnetic oxide was in the range of 1:1 tended to produce clearlyacceptable results while ratios in the order of 2:1 or more tended toproduce marginally acceptable print characteristics at best, unless thecoating weight (the thickness of the ink coating on the ribbon) issubstantially increased. The use of thicker ink coatings on the ribbonis considered very highly undesirable not only because of the potentialextra costs of laying down a thicker coating, but more importantlybecause the thicker coating could result in a substantially reducedfootage of ribbon for a given diameter of spool which is, of course,predefined for a given species of printing equipment.

Attempts to eliminate the use of plasticizer had a highly unexpectedeffect on print quality and the signal transmission. Plasticizer levelson the order of less than about 6% by weight based on the weight of thepolyamide resin tended to have a substantial adverse effect on bothprint quality and signal transmission such that a heavier coat weightwould have to be employed with the disadvantages noted above.Plasticizer levels of about 25% by weight, based on the weight of thepolyamide resin, tended to yield acceptable results from the point ofview of print quality and signal transmission, however, levels aboveabout 25% tend to increase the possibility that the transferred ink willnot be dry to the touch with resultant possibility of smudging. Thus thepreferred range of the plasticizer concentration is from about 6% toabout 25% based on the weight of the polyamide resin, having in mindthat the ratio of resin to magnetic oxide and the specific plasticizerbeing employed could slightly lower or raise the preferred range ofplasticizer concentration.

The present invention also contemplates the use of an optional releaselayer between the aluminum surface of the ribbon substrate and the inklayer. Experiments were conducted with the materials of Example 1 usinga release layer of about 3 microns. Such release layers are prepared bycoating the film with a water based dispersion or emulsion of a highmolecular weight polyethylene, ethylene interpolymers, ethylene vinylacetates and acrylic latex, for example, Adcote 37R610 manufactured byMorton Thiokol, an ethylene interpolymer, and Hycar 26120 manufacturedby B. F. Goodrich which is an acrylic latex.

Use of a release layer had a clearly beneficial effect in diminishingany slight adhesion of particles of the ink layer to the aluminum layer.While the foregoing types of release layers were found to bespecifically effective, such release layers are generally well known inthe non-impact ribbon art and it is expected that any of the knownrelease materials should provide results substantially equivalent tothose achieved with the materials noted above.

It will be understood that the foregoing is presented by way ofillustration and not by limitation and that the wide variety of changes,substitutions can be made in the specific materials processes andequipment hereinbefore described and without departing from the scope ofthe invention herein disclosed.

As in our invention, we claim:
 1. A ribbon for non-impact printing ofdocuments of the type handled by magnetic reader/sorter apparatuscomprising a polycarbonate substrate and a magnetic ink layer with athin film of metal having a thickness of less than about 1200 angstromsdisposed between said substrate and said ink layer, said substrateconsisting essentially of a polycarbonate polymer containing from about20 to about 40 percent by weight of an electrically conductive carbonblack and said magnetic ink consisting essentially of from about 60 toabout 80 parts by weight of a solvent comprising at least memberselected from the group consisting of aliphatic alcohols having from 1to about 5 carbon atoms, and aromatic hydrocarbons having from about 6to about 10 carbon atoms; about 10 to about 30 parts by weight of apolyamide polymer; from about 10 to about 30 parts by weight of amagnetic oxide; from about 1 to about 4 parts by weight of a plasticizerselected from the group consisting of azelate, phthalate, palmitate andadipate esters; from about 0 to about 10 parts by weight of carbon blackand from about 0 to about 5 parts by weight of an erasure proof dye. 2.The ribbon according to claim 1 wherein said metal is a film of vapordeposited aluminum and said ribbon has a thickness of from about 800angstroms to about 1200 angstroms.
 3. The ribbon according to claim 1wherein said ink contains at least from about 5 to about 25% by weightplasticizer based on the weight of the polyamide polymer.
 4. The ribbonaccording to claim 3 wherein said plasticizer is dioctyl azelate.
 5. Theribbon according to claim 1 wherein said ink has a melting point below140° C.
 6. The ribbon according to claim 4 wherein said ink has amelting point of below 140° C.
 7. The ribbon according to claim 1wherein the weight ratio of the polyamide polymer to the magnetic oxideis in the range of from about 4:6 to about 6:4.
 8. The ribbon accordingto claim 1 wherein said solvent comprises a mixture of isopropyl alcoholand toluene.
 9. The ribbon according to claim 8 wherein said alcohol andsaid toluene are present in a weight ratio in the range of from about8:3 to about 3:8.
 10. The ribbon according to claim 1 wherein said dyeis nigrosine dye and is present in the range of from about 0.5 to about4 parts by weight.
 11. A ribbon for non-impact erasure proof printing ofdocuments such as checks negotiable insturments and the like comprisinga polycarbonate substrate and a meltable ink layer with a thin film ofmetal having a thickness of less than about 1200 angstroms disposedbetween said substrate and said ink layer; said substrate consistingessentially of a polycarbonate polymer containing from about 20 to about40 percent by weight of an electrically conductive carbon black; andsaid meltable ink consisting essentially of from about 60 to about 80parts by weight of a solvent comprising at least member selected fromthe group consisting of aliphatic alcohols having from 1 to about 5carbon atoms, and aromatic hydrocarbons having from about 6 to about 10carbon atoms; about 10 to about 30 parts by weight of a polyamidepolymer; from about 10 to about 30 parts by weight of a magnetic oxide;from about 1 to about 4 parts by weight of a plasticizer selected fromthe group consisting of azelate, phthalate, palmitate and adipate estersfrom about 1 to about 10 parts of an erasure proof dye and from about 0to about 10 parts by weight of carbon black.
 12. The ribbon according toclaim 11 wherein said metal is a film of vapor deposited aluminum andsaid ribbon has a thickness of from about 800 angstroms to about 1200angstroms.
 13. The ribbon according to claim 11 wherein said inkcontains at least from about 5 to about 25% by weight plasticizer basedon the weight of the polyamide polymer.
 14. The ribbon according toclaim 13 wherein said plasticizer is dioctyl azelate.
 15. The ribbonaccording to claim 12 wherein said ink has a melting point below 140° C.16. The ribbon according to claim 11 wherein the weight ratio of thepolyamide polymer to the magnetic oxide is in the range of from about4:6 to about 6:4.
 17. The ribbon according to claim 11 wherein saidsolvent comprises a mixture of isopropyl alcohol and toluene.
 18. Theribbon according to claim 17 wherein said alcohol and said toluene arepresent in a weight ration in the range of from about 8:3 to about 3:8.19. The ribbon according to claim 11 wherein said dye is nigrosine dyeand is present in the range of from about 1.0 to about 5.0 parts byweight.